84 
CONSTRUCTION OF HOT-HOUSE ROOFS, 
In each valley of the angles two large screws are inserted into the styles of the 
lights to fasten them firm. Air is admitted by sliding the front sashes, and by 
ventilators in the back wall 
(o), which are made to swing 
on pivots, and open by means 
of long iron rods, having holes 
to fix on pins driven in the 
wall, so as to regulate the pro- 
portion of air at pleasure (p). 
To prevent these ventilators 
from being unsightly, a square 
piece of trellis-work is placed 
over the opening inside the 
house, as may be seen in the 
perspective view. 
if 
The sash bars, both of the roof and front lights 
do not obstruct much light, as from their size, 
shown in the sketch a, being the full size of the 
bars in the roof-sashes, and h the size of those in 
the front ones, very little shade can be made by 
them. The grooves where the glass fits in, pre- 
vents the putty shelling off, or the wet making 
its way betwixt the putty and wood, and the 
difficulty of glazing, when any squares are broken, 
is trifling. 
The house is heated by four fires ; the flue covers are dished, for the advantage 
of steaming. The two end flues run under the front walk, and meeting in the 
middle of the house, cross and discharge themselves at the two chimneys in the 
centre of the back wall ; and the two centre flues pass under the centre walk, and 
discharge themselves at the two end chimneys. 
The walks are three feet six inches wide, and are composed of bars of wood 
four inches broad, and an inch and a half thick, nailed half an inch apart upon 
strong bearers. 
The price for the erection stands as follows : — deal wood, taking an average, 
including the scantling, &c., &c, will scarcely exceed 2^d. per foot ; sawing the 
same, 4<y. per hundred feet ; workmanship, 2^d. per foot ; glass, six inches by 
